The subject matter of the invention relates generally to centrifugally operable speed-responsive devices and more particularly to the operation of an electrical switch unit or stationary switch of the type used for the starting winding circuits of fractional horsepower motors. In my prior U.S. Pat. Nos. 2,616,682; 2,768,260 and 3,793,891 I have provided a detailed and thorough description of the environment in which such devices are utilized and the problems encountered in obtaining uniform operating characteristics and precise operating control. In said U.S. Pat. No. 2,768,260, I have discussed the various factors involving cumulative assembly and manufacturing tolerances which could significantly affect the operating characteristics of such a speed-responsive switching device. Reference is made to the foregoing patents for a fuller discussion of such devices.
It may be noted that the centrifugally-actuated switching devices referred to in the foregoing prior patents, all utilize orbiting weights to flex a snap-action spring to which a switch-engaging spool is secured. Normally the spring projects the spool against the resilient contact arm of the stationary switch to maintain the starting winding circuit of the motor closed when the motor is in the static or non-running condition. After the motor is energized and attains a sufficiently high speed to no longer require the starting torque advantages of the starting winding circuit, the orbiting masses or weights cause snap action of the spring to retract the spool from the stationary switch and open the circuit to the starting winding. The spool moves longitudinally or axially toward and away from the contact arm of the stationary switch in response to the action of the spring. When the motor is deenergized or if for any other reason its speed is drastically reduced, the orbiting weights lose energy and the force of the spring is eventually sufficient to overcome the action of the weights and snap back the spool to its switch-engaging static position. The switch-actuating spool moves contemporaneously and directly with the longitudinal movement of the spring, so that the entire action of the spool is one of longitudinally directed movement over the range of longitudinal displacement accomplished by the spring. The centrifugally-induced movement of the weights which cause deflection of the spring have an indirect effect through the spool on the operation of the stationary switch; but there is no direct engagement of the weights with the stationary switch.
As discussed in the prior art patents, particularly U.S. Pat. No. 2,768,260, the spacing between the stationary switch and the centrifugal device is critical in obtaining the desired speed-responsive characteristics and this spacing does vary due to cumulation of manufacturing tolerances and assembly tolerances in commercial production.
Another problem can be characterized as "contact bounce" and "flutter" both of which can and do occur when assembly tolerances cumulate to the point where a positive closing action of the stationary switch is not uniformly attainable. Inasmuch as the reaction force of the stationary switch contact arms does have an effect on the cut-out and cut-in speeds of the centrifugal unit, any flutter or contact bounce necessarily produces non-uniformity in the operating speeds of the centrifugal unit and in its snap-action characteristics.